wrt54g going crazy - network comes to a halt

I have a WRT54G v6. This thing runs my network in a hotel, and provides access to the Internet for our guests. I also have 2 WAP54G, and another WRT54G behind this main router, but these other ones don't do NAT or DHCP functions; they just provide access to the network and to the Internet. I estimate about 10-20 computers being active at any given time, and have about 100 of them registered with an IP address in the DHCP table. I had no problem with it ever since it was set up last year.

All of a sudden, the things stops giving out IP addresses. You plug in a computer to the network, and can't obtain an IP address. You get this "limited or no connectivity" message.

After finding it on several computers, I can rule out cabling problems. Also, if you set a static IP address on a computer, it'll have no problem accessing the Internet via this router.

When I reset it, it works for a while. For how long? 5 minutes to about 4-6 hours. Then halts again. You can still access the Internet if you have a proper static IP address configured on your computer.

Originally, I had this network set up with a wired BEFSR81 v2 router up until 2-3 days ago, when this problem started. After some trouble-shooting, I replaced that with this newer WRT54G v6. No joy. I flashed the firmware, I even installed DD-WRT on it, with no luck whatsoever. I know a businessman came just about the same time when this started, and he is trying to do a LOT of ftp up and down. That's the only thing I can correlate to my problems, but I can't tell him to not use it for a day a see what happens. Also, ftp shouldn't halt the router's DHCP feature...

I installed Wireshark to look at my network, but from those packets I see, I don't know what's normal and what's not. I'm not that much trained to make too much sense out of those packets.

I looked at the possibility of maybe some guest plugged in some device that conflicts with my Linksys (maybe another DHCP server on my network), but couldn't find one...

The router is configured with a static WAN address that I got from my ISP, pretty much everything else is factory default of DD-WRT. The wireless feature is turned off. No QoS, no DMZ, and no UPnP turned on. No port-forwarding, nothing.

Maybe one of your guests is overloading the connection table.
Those routers need to keep track of all connections for a while. Default firmware tracks for a week and only has 2000 connections. With a 3rd party like DD-WRT, you can allow to track 4096 connections and limit the tracking time to 5 or 10 minutes.
Check what your setting is. Limit the tracking time to the minimum and the connection numbers to the max. If your contrack table is full, the router cannot open new connections, even on its LAN, and it just sits there, useless...